Long-term isolated renal perfusion has been accomplished in dog kidneys with maintenance of excellent renal blood flows, glomerular filtration rates, and reabsorptive capacities for salt and water. This preparation is used for studies of humoral factors which may help govern intrarenal hemodynamics and secondarily affect renal function. Thus, data are accumulated concerning the interrelated physiology of the renin-angiotensin system, prostaglandins, and kinins with changes in renal blood flow, distributions of intrarenal blood flow, and alterations in renal perfusion pressure. An isolated liver-kidney preparation has been devised which allows a further evaluation of the influence of the liver on renal hemodynamics.